At the risk of looking completely foolish…
As a newbie to playing the flute I have noticed myself making grunting noises into the flute whilst actually blowing (not quite as bad as the female tennis players) unintentionally, probably where notes would be tongued. Has anyone else had this problem and how have you overcome it? Not quite as easy as just telling myself not to do it!!
Ade
well it’s that easy from here!
ah, as a general rule, don’t do it.
In ITM, don’t do it.
Sometimes in jazz and or rock it’s okay…Ian Anderson
Open throat…
Sub-vocalization … grunting … is not unknown even among experienced players, though maybe not so much on winds. I recall recordings by fiddler Dave Swarbrick where he’s grunting and moaning up a storm. I tend to grunt when playing non-winds - box, concertina, guitar - but, oddly enough, mostly in private. When playing in public, it mostly goes away. I suspect that the unconscious embarrassment throttle kicks in.
If you’re not used to playing with others, maybe the problem will subside when you get more experience in public playing. Meanwhile, pretend like you have an audience of friends watching you. And it really is what you said. Just be aware, and tell yourself to stop. Discipline is part of learning. 
Good luck …
This occasionally happens to us all.
Just think of them as flute farts. 
–James
Yup, Denny’s got it right!
The “grunting” sound comes from deep down in your throat.
Therefore, and hereafter, please remind yourself to KEEP YOUR THROAT OPEN.
Besides, there are other advantages to doing so.